Consolidated Statements of Convertible Preferred Stock and Stockholders’ Deficit - USD ($)	Common Stock IPO	Common Stock	Additional Paid-in capital IPO	Additional Paid-in capital	Accumulated other comprehensive loss	Accumulated deficit	Series A convertible preferred stock	Series B convertible preferred stock	Series C convertible preferred stock	IPO	Total
Temporary equity, beginning balance at Dec. 31, 2017							$ 6,483,044	$ 49,742,942
Temporary Equity, Beginning Balance (in shares) at Dec. 31, 2017							612,446	7,235,969
Increase (Decrease) in Temporary Equity
Issuance of convertible preferred stock, net of issuance costs									$ 56,364,645
Issuance of convertible preferred stock (in shares)									4,712,698
Temporary equity, ending balance at Dec. 31, 2018							$ 6,483,044	$ 49,742,942	$ 56,364,645
Temporary Equity, Ending Balance (in shares) at Dec. 31, 2018							612,446	7,235,969	4,712,698
Equity, beginning balance at Dec. 31, 2017		$ 126,838		$ 19,335,560	$ (8,287,406)	$ (46,940,187)					$ (35,765,195)
Equity, beginning balance (in shares) at Dec. 31, 2017		1,153,061
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		$ 253		1,844							2,097
Exercise of stock options (in shares)		2,305
Stock‑based compensation				329,184							329,184
Foreign currency translation					(473,919)						(473,919)
Net loss						(15,528,269)					(15,528,269)
Equity, ending balance at Dec. 31, 2018		$ 127,091		19,666,588	(8,761,325)	(62,468,456)					(51,436,102)
Equity, ending balance (in shares) at Dec. 31, 2018		1,155,366
Increase (Decrease) in Temporary Equity
Issuance of convertible preferred stock, net of issuance costs									$ 5,598,362
Issuance of convertible preferred stock (in shares)									467,179
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		$ 3,179		67,818							70,997
Exercise of stock options (in shares)		322,267
Issuance of common stock	$ 6,517		$ 86,899,563	100						$ 86,906,080	100
Issuance of common stock (in shares)	6,516,667	160
Stock‑based compensation				1,345,722							1,345,722
Foreign currency translation					(2,772,453)						(2,772,453)
Exchange of preferred and common stock of Aprea Therapeutics AB into stock of Aprea Therapeutics, Inc.		$ (128,792)		128,792
Conversion of preferred stock into common stock		$ (13,028)		(118,175,965)			$ 6,483,044	$ 49,742,942	$ 61,963,007		(118,188,993)
Conversion of preferred stock into common stock (in shares)		13,028,292					(612,446)	(7,235,969)	(5,179,877)
Net loss						(28,059,807)					(28,059,807)
Equity, ending balance at Dec. 31, 2019		$ 21,023		226,284,548	(11,533,778)	(90,528,263)					124,243,530
Equity, ending balance (in shares) at Dec. 31, 2019		21,022,752
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		$ 164		150,785							150,949
Exercise of stock options (in shares)		164,075
Stock‑based compensation				4,983,023							4,983,023
Foreign currency translation					1,496,517						1,496,517
Net loss						(53,478,812)					(53,478,812)
Equity, ending balance at Dec. 31, 2020		$ 21,187		$ 231,418,356	$ (10,037,261)	$ (144,007,075)					$ 77,395,207
Equity, ending balance (in shares) at Dec. 31, 2020		21,186,827